1. Field of the Invention
This invention relates to a heating apparatus causing no pollution of solution or gas in the beating of a high purity solution such as an ultra pure water, a sterilized water or the like; a solution containing a strong acid ion such as aqua regia; a reactive and high a corrosive gas such as CF4, NF3, ClF3, HF or the like; and so forth as well as a high purity corrosion-resistant member applied thereto.
2. Description of Related Art
In case of heating the solution such as the ultra pure water, the sterilized water or the like, a heater coated with a polytetrafluoro-ethylene (Teflon, trade name) is used for preventing the pollution of such a solution. Concretely, there is known a method wherein the heater is formed by coating a surface of a rod-shaped metal heating element with Teflon and placed in a container including the solution; or a method wherein an inner wall face of the container is coated with Teflon and heated from an exterior. At recent, it is demanded to heat a ultra-high purity corrosive solution containing hydrofluoric acid, nitric acid, hydrochloric acid or a mixed acid such as aqua regia in addition to the ultra pure water or the sterilized water without causing pollution through a metal ion or an organic matter.
In the latter case, Teflon is modified by the acid ion and hence Teflon is swollen to peel from the metal heating element or the container, or molecules in the solution permeate through Teflon. As a result, a metal ion from the metal heating element or the container pollutes the solution to be treated, or Teflon itself elutes therefrom, so that the apparatus can not be used for a long time.
In order to solve this problem, if the thickness of the Teflon coating is made thicker, since the thermal conductivity of Teflon is low, the heating efficiency becomes extremely low. And also, the heating can not be conducted at a higher temperature because the heat-resisting temperature of Teflon is about 300xc2x0 C. Further, if a high inner pressure is applied to the container, the strength of the container coated with Teflon itself is required to be high and hence the thickness of the container becomes thicker. In this case, if the heating portion is arranged outside the container, it is impossible to rapidly heat the corrosive solution therein.
It is, therefore, an object of the invention to provide a heating apparatus for receiving and heating a corrosive substance, which is high in the corrosion resistance to the corrosive substance and good in the heat efficiency in the heating of the corrosive substance and can rapidly heat the corrosive substance without polluting the corrosive substance.
It is another object of the invention to provide a corrosion-resistant member usable for the above heating apparatus and a method of manufacturing the same.
According to a first aspect of the invention, there is the provision of a corrosion-resistant member comprising: a substrate of a ceramic having a resistivity at room temperature of not less than 5000 xcexa9xc2x7cm, and a silicon carbide film formed through a chemical vapor deposition process and covering at least a surface of the substrate exposed to a corrosive substance and having a resistivity at room temperature of 20-500 xcexa9xc2x7cm.
According to a second aspect of the invention, there is the provision of a method of manufacturing a corrosion-resistant member by forming a silicon carbide film on a substrate through a chemical vapor deposition method, in which hydrogen is fed at a film-forming temperature, and then at least one silicon-supplying compound selected from the group consisting of SiCl4, SiHCl3, SiH2Cl2 and SiH4 and at least one carbon-supplying compound selected from the group consisting of CH4, C2H6 and C3H8 are fed.
According to a third aspect of the invention, there is the provision of a method of manufacturing a corrosion-resistant member by forming a silicon carbide film on a substrate through a chemical vapor deposition method, in which when a mixed gas of at least one silicon-supplying compound selected from the group consisting of SiCl4, SiHCl3, SiCl2H2 and SiH4, at least one carbon-supplying compound selected from the group consisting of CH4, C2H6 and C3H8, H2 and Ar is used as a starting gas, the following relations are satisfied in the starting gas:
0.14xe2x89xa6([A]+[B]xc3x97n)/([Ar]+[H2])xe2x89xa60.55
1.0xe2x89xa6[A]/([B]xc3x97n)xe2x89xa61.6
0.09xe2x89xa6[Ar]/[H2]xe2x89xa65
wherein n is a carbon atom number per one molecule of the carbon-supplying compound, [A] is a volume of the silicon-supplying compound converted to gas at a standard state, [B] is a volume of the carbon-supplying compound converted to gas at a standard state, [Ar] is a volume of the argon converted to gas at a standard state, and [H2] is a volume of the hydrogen converted to gas at a standard state.